This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-216987, filed Jul. 17, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a high-voltage semiconductor device used as a switching element for a power device or the like.
2. Description of the Related Art
The structure and characteristics of a high-voltage diode and high-voltage transistor serving as conventional high-voltage semiconductor devices will be described below.
FIG. 1 is a sectional view showing the structure of a conventional high-voltage diode.
As shown in FIG. 1, a high-resistance nxe2x88x92-type epitaxial layer 102 is formed on one surface of a low-resistance n+-type semiconductor substrate 101. A low-resistance p+-type anode layer 103 is formed on the nxe2x88x92-type epitaxial layer 102. An anode electrode 104 is formed on the p+-type anode layer 103. An anode terminal A is connected to the anode electrode 104.
A cathode electrode 105 is formed on the other surface of the n+-type semiconductor substrate 101. A cathode terminal K is connected to the cathode electrode 105.
In the high-voltage diode having the structure shown in FIG. 1, a depletion layer spreads from the p+-type anode layer 103 to the inside of the nxe2x88x92-type epitaxial layer 102. This relaxes an electric field in this region, thereby implementing a high breakdown voltage.
When a reverse bias is applied, as shown in FIG. 2, such a high-voltage diode exhibits an electric field distribution in which an electric field is uniformly reduced from the anode side to the cathode side. To realize a necessary breakdown voltage, the thickness of the nxe2x88x92-type epitaxial layer 102 must be increased. However, when the thickness of the nxe2x88x92-type epitaxial layer 102 is increased, an ON resistance increases. An increase in ON resistance similarly occurs when this structure is applied to a MOS field effect transistor (to be referred to as a MOSFET hereinafter).
To solve this, a high-voltage diode shown in FIG. 3 which can obtain a high breakdown voltage without increasing an ON resistance is proposed. This high-voltage diode has the following structure.
As shown in FIG. 3, trenches which extend from the upper surface of the p+-type anode layer 103 to the n+-type semiconductor substrate 101 are formed in the p+-type anode layer 103 and nxe2x88x92-type epitaxial layer 102. An oxide film 106 is formed on the inner wall of each trench. A semi-insulating high-resistance element 107 is buried in each trench in which the oxide film 106 is formed.
The high-voltage diode shown in FIG. 3 has the oxide film 106 between the nxe2x88x92-type epitaxial layer 102 and high-resistance element 107. A large-capacitance capacitor is thus formed between the nxe2x88x92-type epitaxial layer 102 and high-resistance element 107. Letting R be the resistance of the high-resistance element 107, and C be the capacitance of the capacitor, a CR time constant at the start of operation increases, and depletion layer formation takes a long time, thereby making a leakage current keep flowing until the depletion layer formation ends. This means that a long time is required for obtaining dielectric breakdown. Consequently, when a high voltage is abruptly applied between the anode terminal A and cathode terminal K at the start of operation, sometimes the leakage current increases to damage the high-voltage diode.
In addition, after forming the trenches in the nxe2x88x92-type epitaxial layer 102, the high-voltage diode shown in FIG. 3 requires the step of oxidizing the inner walls of the trenches and then removing the oxide films on the bottom surfaces of the trenches. This results in the manufacturing disadvantage of the high-voltage diode.
A semiconductor device according to an aspect of the present invention comprises: a first-conductivity-type semiconductor region formed on a first-conductivity-type semiconductor body, the first-conductivity-type semiconductor region having an electric resistance higher than that of the first-conductivity-type semiconductor body; a second-conductivity-type semiconductor region formed on the first-conductivity-type semiconductor region; and a high-resistance region formed in the first-conductivity-type and second-conductivity-type semiconductor regions, the high-resistance region being in contact with the first-conductivity-type and second-conductivity-type semiconductor regions and extending from an upper surface of the second-conductivity-type semiconductor region in a direction of the first-conductivity-type semiconductor body.